1. Field of the Invention
The present invention relates to a method and an apparatus for preparing a toner used as developer developing electrostatic latent images in electrophotography, electrostatic recording and electrostatic printing, and a toner prepared thereby; and more particularly to improvement of uniform particle diameter dispersibility of the toner and productivity thereof.
2. Discussion of the Related Art
Developers for use in electrophotography, electrostatic recording and electrostatic printing, in their developing processes, are transferred to image bearers such as photoreceptors electrostatic latent images are formed on, transferred therefrom to a transfer medium such as a transfer paper, and fixed thereon. As the developers for developing electrostatic latent images formed on image bearers, a two-component developer including a carrier and a toner, and a one-component developer without a carrier, such as a magnetic toner and a nonmagnetic toner, are known.
Conventionally, as a dry toner for use in electrophotography, electrostatic recording and electrostatic printing, a pulverized toner is widely used, which is formed by kneading a toner binder such as styrene resins and polyester resins with a colorant, etc. upon application of heat, cooling the kneaded mixture to be solidified and pulverizing the solidified mixture.
Recently, polymerized toners prepared by suspension polymerization methods, emulsion polymerization condensation methods, etc. are being used. Besides, Japanese published unexamined application No. 7-152202 discloses a polymer solution suspension method of using a volume contraction. This method includes dispersing or dissolving toner constituents in a volatile solvent such as an organic solvent having a low boiling point to prepare a dispersion or a solution, emulsifying the dispersion or solution in an aqueous medium to form a droplet, and removing the volatile solvent. The diversity of resins this method can use is wider than those of the suspension polymerization methods and emulsion polymerization condensation methods, and has an advantage of being capable of using a polyester resin effectively used for full-color images requiring transparency and smoothness.
However, in the polymerization methods, since a dispersant is basically used in an aqueous medium, the dispersant impairing the chargeability of a toner remains on the surface thereof, resulting in deterioration of environmental resistance. In addition, a large amount of water is needed to remove the dispersant, resulting in unsatisfactory methods of preparing a toner.
Japanese published unexamined application No. 57-201248 discloses a spray dry method having been known from long ago as a method of preparing a toner without using an aqueous medium. This atomizes and discharges a toner constituent solution or a toner constituent liquid with various atomizers, and dries to form particles. Therefore, this does not have problems o using an aqueous medium. However, particles prepared by the conventional spray granulation methods are coarse and large, and have a wide particle diameter distribution, resulting in deterioration of toner properties themselves.
Japanese Patent No. 3786034 discloses a method and an apparatus forming a microscopic droplet of a toner constituent with a piezoelectric pulse, and drying and solidifying the microscopic droplet to form a toner. Further, Japanese Patent No. 3786035 discloses a method of forming a microscopic droplet thereof with a heat expansion in a nozzle, and drying and solidifying the microscopic droplet to form a toner.
A method disclosed in Japanese published unexamined application No. 2006-293320 is that a nozzle is oscillated by expansion and contraction of a piezoelectric body as an oscillator to discharge a toner constituent fluid droplet at a constant frequency, and that the droplet is solidified to from a toner.
In the methods disclosed in Japanese Patents Nos. 3786034 and 3786035, and Japanese published unexamined application No. 2006-293320, since the toner constituent has high viscosity and includes particulate materials, the toner constituent adheres to a circumference of the nozzle discharging a microscopic droplet to downsize its diameter and frequently clog the nozzle.
Nozzles of civilian goods such as an inkjet recorder are typically subjected to a periodical maintenance to prevent the nozzles from being clogged or clear the nozzle. However, it is impossible to stop the operation to subject the nozzles for preparing a large amount of a microscopic powder such as a toner to maintenance every time when clogged in terms productivity. In addition, the nozzles discharging a toner constituent having high viscosity are much more frequently clogged than those of the inkjet recorders.
Further, a number of nozzles need to be located on a reservoir of the toner constituents to prepare a large amount of a toner. When a part of the nozzles is clogged, the sprayability of the other nozzles are adversely affected, resulting in uneven particle sizes of the resultant toner.
Because of these reasons, a need exists for a method of stably preparing a toner having a uniform particle size.